1. Field of the Invention
The invention relates generally to improvements in devices for sharpening blades that are used for cutting grass, sod, or other plant matter. More particularly, the invention pertains to an apparatus incorporating an extensible, retractable, and rotationally adjustable multi-axis support assembly for a rotary grinder, and a blade holding fixture that maintains the workpiece at a predetermined angle for grinding.
2. Description Of the Prior Art
The prior art includes a number of approaches directed toward the task of sharpening mower blades. For example, U.S. Pat. No. 7,918,715, issued to Clark et al., discloses a Device And Method For Sharpening Blades. A fixture in the '715 Patent, holds the blade to be sharpened in the desired position. An elevated horizontal shaft is slidably coupled by a handle bar whose end adjustably supports a rotary grinder.
In U.S. Pat. No. 6,761,623, granted to Baker, an Apparatus And Method For Sharpening Blades At A Predetermined Angle, are disclosed. Included in Baker's apparatus are a blade retention and positioning mechanism, a blade sharpening mechanism, and a guide rod for directing the blade sharpening mechanism laterally across the width of the apparatus.
Yet another Blade Sharpener employing a rotary grinder is shown in U.S. Pat. No. 7,967,666, issued to Messner. Messner's sharpener employs a blade support, a sharpener guide mounted to the blade support, and a sharpener mount. A rotary grinder is mounted on the end of the sharpener mount, so that the sharpener mount and the grinder may pivot about a sharpening axis to provide the desired sharpening angle on the blade, while allowing translational movement along the sharpening axis for sharpening the full extent of the cutting edge of the blade.
And, in U.S. Pat. No. 7,329,172, issued to Dieck et al., a Rotary Mower Blade Sharpener Having Movable Grinding Wheels is illustrated. The mower blade is mounted on a base plate. Grinding head assemblies are mounted on carriages slidably mounted on a respective rail. The rails are parallel to each other, and located on either side of the blade. The carriages are driven by an endless chain that moves them and the grinding assemblies in unison, so that the two opposing cutting edges of the blade can be simultaneously sharpened.
Another approach to sharpening mower blades is to maintain the grinding apparatus stationary, and then move the cutting edge of the mower blade into and out of engagement with the abrasive wheel of the grinding apparatus. Representative of this approach is the device shown in U.S. Pat. No. 6,786,806, granted to Maus, Jr. The '806 Patent discloses a Rotary Mower Blade Sharpener using a conventional bench grinder in combination with a mower blade holder. As shown in FIGS. 1 and 2, the subject blade is slid into and out of engagement with the grinder's wheel.
Similarly, in U.S. Pat. No. 6,471,569, granted to Bernhard, a Rotary Mower Blade Grinder includes an adjustable support for receiving a rotary mower blade. The position of the blade is movable and adjustable, axially and transversely, to engage a grinding wheel 4.
U.S. Pat. No. 4,736,544, issued to Greenquist, teaches a Blade Holder For Sharpening Lawnmower Blades. Grinder 52 is fixed in position, and the blade support plate 12 is movable, as explained in column 4, lines 5-9 of this reference.
An Apparatus For Sharpening Implements is disclosed in U.S. Pat. No. 5,218,787, granted to Rice. A conventional grinder 12 is mounted on a support post 34. The apparatus has a movable carriage for holding the blade by means of a clamping wrench, so the blade can selectively be moved into engagement with a grinding wheel 22.
Issues regarding the performance of prior art blade sharpening devices include inadequate means for precisely adjusting and maintaining the angle of the grinding wheel during the grinding process. Known prior art blade sharpening devices also lack features for securely maintaining the subject blade at a selected predetermined angle, so the cutting edge can be faithfully restored to manufactured specifications. And, such prior art devices do not include simple and reliable means for positioning, locking, and releasing blades in a blade holding fixture, specifically designed for sharpening a blade having either two opposing cutting edges, or a blade having a single edge with a complex cutting edge contour.
Therefore, it is an object of the apparatus disclosed herein to sharpen blades used for mowing, having different angles and contours for their cutting edges.
It is a further object herein, to mount and utilize a conventional rotary grinder within a rotatable, extensible, and retractable support assembly.
It is also an object herein to support a rotary grinder adjustably about three axes and along one axis for extension and retraction.
It is also an object herein detachably to position and secure a mower blade at a number of different predetermined angles, for sharpening the cutting edge properly.
These and other objects will become apparent in the specification and the detailed description of the preferred embodiment, to follow.